1. Field of the Invention
This invention relates to joints, specifically to a joint using a combination of hydraulics and gears to convert linear hydraulic motion into radial motion and thereby provide both variable extension assist, as well as an infinite number of flexion stops for controlled flexion flow. Applications may include, but are not limited to, joints for orthotic devices which facilitate the extension and flexion of an inadequately functioning human joint, such as a knee. The compact configuration of the present invention would provide the cosmetic advantage of allowing such orthotic devices to fit more easily under clothing wherein they would be less noticeable during use. The present invention joint also has the enhanced strength, enhanced operational efficiency, decreased stress and wear on moving components, and enhanced user comfort and security over the majority of prior art joints used in similar applications. The present invention compact two-axis joint comprises a main member, a distal member, a hydraulic cylinder and piston, a drive gear, and a thickened transfer gear. The distal member has a cut-out area located close to its proximal end and a portion of the thickened transfer gear is press-fit into the cut-out area, leaving the remainder of the transfer gear not press-fit into the cut-out area for interaction with teeth on the drive gear. The opposed end of the distal member is configured for connection to orthotic hardware secured to the lower portion of a body limb. During present invention use for orthotic applications, two independently functioning present invention joints are typically used, one on each side of the inadequately functioning human joint. The hydraulic cylinder, piston, and drive gear are associated with the main member, with the drive gear configured and positioned near its proximal end for providing radial force transfer between the hydraulic piston and the transfer gear. The main member further has an end opposed from the drive gear that is configured for connection to orthotic hardware secured to the upper portion of a body limb. When the present invention joint is in its fully extended orientation, the distal member extends from the main member in a direction substantially opposite to that of the main member. Furthermore, movement of the distal member relative to the main member between positions of complete flexion and full extension is approximately the full 135-degree range of anatomical motion, resulting in an approximate 45-degree angle between the distal member and the main member when the distal member is in a position of complete flexion relative to the main member. The present invention's hydraulic piston, in combination with the drive gear and transfer gear that provide a functional gear ratio (often a 2:1 gear ratio in orthotic applications), allows the use of a smaller hydraulic cylinder (and less piston travel). A spring biasing member is located in a remote control valve assembly, allowing the use of a much larger spring while being less noticeable. Furthermore, a two axis (co-linear) construction that further enhances joint strength and compactness is used for the pivotal connection between the distal member and the main member.
2. Description of the Related Art
Particularly in the field of orthotic devices relating to the support of a human knee, there is a need for a joint which can assist in the forward movement of a person's lower leg and foot, and which will also exhibit a controlled flexion moment at the knee once the person's foot is planted on a floor or ground surface and his or her weight is shifted forward over the joint. For social acceptability, it is also desirable to have orthotic devices which are minimally obtrusive. Many joints are known which comprise varying combinations of springs, gears, levers, and cables and which can hold a joint in a limited number of angles of flexion and provide a limited amount of extension assist. However, none provides all of the advantages of the present invention that derive from the combined use of hydraulic forces, two gears providing a gear ratio, and a two-axis (co-linear) construction. It is not known to have a cosmetically advantageous and compactly designed joint which provides adjustable extension assist, as well as an infinite number of flexion stops to prevent sudden collapse of the joint under a shifting weight load, through the combined use of hydraulic forces and gears that radially transfer the linear hydraulic forces applied. In addition in orthotic applications, components used should be compact and minimally intrusive for ease of use, enhanced social acceptability, and a lessened risk of hazard or damage during use. Further, a user should not experience insecurity, discomfort, or apprehension as a result of any aspect of orthotic device performance. As a fundamental part of their construction, all joints used in orthotic devices must include design features and/or apparatus that define the limits of their flexion and extension, and movement provided therebetween should avoid excesses and insufficiencies of motion. Often, mechanical joints are bulky in configuration, provide an abrupt stop for the user, and/or fail to provide proper support for a user when the joint nears maximum extension. Orthotic devices should also be as simple as possible for ease of manufacture and convenience during their function. The use of a hydraulic piston in combination with two gears provide improved interior design that is new in the field of orthotic joints, and produce a functional gear ratio (preferably 2:1 or close thereto in many applications) that allows less hydraulic piston travel. Furthermore, the distal member and the main member are pivotally connected to one another using a two-axis (co-linear) construction that provides further compactness and operational efficiency in the present invention joint. No other joint is known to have the same structure, function in the same manner, or provide all of the advantages of the present invention.